Electric fuse



Patented Jan. 12, 1943 ELECTRIC FUSE Morris B. Wood, Newbury, Mass., assgnor to The Chase-Shawmut Company, Newburyport, Mass., a corporation of Massachusetts Application January 11, 1941, Serial No. 374,101

(Cl. 20D-131) 15 Claims.

This invention relates to cartridge-type electric fuses and particularly kto the venting thereof.

The satisfactory venting of an enclosed fuse presents a considerable problem. The fuse casing cannot be sealed as the pressure internally thereof resulting from the heavy current interrupting arc may burst the casing. The casing must not be freely vented as dangerously hot gases may be discharged therefrom and the internal pressure may not be high enough to cause the circuit interrupting arc to be extinguished promptly. Thus the venting must be restricted and a rather close adjustment of the venting must be provided. AThe degree of venting should not change materially during the ventinat action. Hence the venting passage should not be materially affected by the products discharged through the vent. The character of the vent should be such that the resistance to the discharge of the products of circuit interruption readily can be duplicated closely in identical fuses so that the performance of all identical fuses will be the same.

An object of the invention is a cartridge-type fuse having improved means for venting the interior of the enclosing casing to relieve the casing from high pressures incident to the interruption of heavy excess currents while at the same time liberating only Vrelatively cool gases.v

A further object of the invention is yan enclosed fuse having venting mechanism that can be made accurately and economically -and so that a large number of duplicate fuses will have the same venting characteristics.

rIn accordance with the present invention the venting structure comprises two closely confronting surfaces, preferably cylindrical or radial Afor ease of manufacture, between which the products of circuit interruption pass, one of the vsurfaces having a succession of grooves, with intervening lands, and the gases discharging successively ,into these grooves and expanding and eddyingtherein, thereby losing velocity, energy and temperature in their passage through the venting structure. Such a structure constitutes a further object of the invention and permits the rspacing between the surfaces to be considerablygreater than if the expansion grooves were omitted so that the structure is not liable to variations of performance during the progress of venting, or due to manufacturing inaccuracies,

A yet further object of the invention resides generally in improving enclosed fuses andthe venting thereof.

Fig. 1 is a longitudinal section through a cartridge fuse of the knife blade type embodying the present invention.

Fig. 2 is an elevation of the left hand end of the fuse of Fig. 1.

Fig. 3 is an elevation of the right hand end of the fuse of Fig. 1. I

Fig. 4 is an exploded perspective view of the left hand knife blade structure of the fuse of Fig. 5 is an exploded perspective view of the right hand knife blade structure of the fuse of Fig. l, illustrating particularly the construction of the venting member.

Fig. 6 is a plan view of the right hand knife blade structure of Fig. 1, removed from the enclosing casing.

Fig. 7 is an enlarged sectional detail of the disc assembly and nipple at the right hand end of Fig. '1.

Fig. 8 is a longitudinal sectional detail through a knife rblade terminal rillustrating a modied form of venting structure.

Fig. 9 is a longitudinal sectional detail through one end part of a ferrule-type cartridge fuse, illustrating the venting principle of Fig. 1 applied to such type of fuse.

Fig. 10 is a view similar to Fig. 8 but illustrating a modified form of venting structure.

Fig. 11 is a sectional View of an end cap having a further modified form of venting structure, adapted to fit the fuse casing of Figs. 9 and 10.

In Figs. 1 through 6, the invention is associated with a knife blade cartridge fuse having the tubular fibre enclosing casing i6 provided with internal screw threads I8 yand 20 at the ends thereof which mesh with external screwthreads 22 of end nipples 24 and 26, respectively, having annularly outstanding cylindrical shoulders 28 and 3e which are seated against the .end faces of the casing i6. The shoulder 28 has external screw threads 3l which mesh with internal screw threads 32 of a removable end cap 34 provided at its outer end with an internally extending annular yiiange 36 that extends inwardly of the screw threads and confronts the end face of the shoulder 28 and surrounds a cylindrical opening 38.

The nipple 24 has a cylindrical axial passage 40 therethrough and the nipple 25 has a. cylindrical axial passage 62 therein which can extend completely therethrough except that, preferably, at the outer end thereof the nipple is provided with an inwardly directed annular flange or shoulder-44 surrounding an annular axial opening 46. Both nipples 'are preferably of metal and the nipple 26 especially is preferably of metal of good hea-t conductivity. The passages 40 and 42 of the nipples' can be of equal diameter. At least the passage 42 of the nipple 26 is not smaller in diameter' than the diameter of the passage 40 of the nipple 28.

The removable fuse link carrying structure includes the terminal knife blades 48 and 5D connected by the interposed straight insulating bar 52 usually of nbre.

The knife blades are generally similar in that both have wide flat outer portions and nar rower inner portions or tongues 54 and 56 with oppositely extended shoulders 58 and 60, respectively, at the juncture of the wide and narrow portion. The tongues of the blades are connected to the ends of the fibre bar 52, and each blade is secured rigidly to the bar by screws 64 and rivets 66. A screw 68 is screw-threaded into each tongue and serves to connect a fusible link 'l to the knife blades.

The knife blade 48 carries a circular disc 'i2 thereon which has a rectangular slot 74 therethrough through which the tongue 54 is extended, the outer face of the disc being seated against the opposed shoulders 578. The blade 48 also carries a smaller circular disc T6 which has a rectangular slot 18 through which the tongue 54 is extended, the disc 16 seating upon the inner face of the disc 12. The two discs are fixed firmly to the knife blade and against each other and the shoulders 58 in any suitable manner as by forcing the material adjacent the slot in the smaller disc 16 against or into the tongue of the knife blade.

The large disc 12 has a diameter such that it can freely enter the end cap 34 and overlie the inner face of the ange 36 thereof and also overlie and engage the outer face of the nipple 24. Thus when the end cap is screwed home'the disc 'I2 is clamped against the nipple 24 and the entire removable assembly is held against axial movement.

The smaller disc 'I6 is adapted removably to enter, and has a diameter about equal or but slightly less than that of the passage 40 through the nipple 24 and thus centers the removable assembly within the enclosing casing and holds it against undue lateral movement in the enclosing casing- The tongue 5G of the right hand knife blade 50 is extended through rectangular holes 1S in a series of large circular discs 80 and alternate small circular discs 82. The discs of the collection are seated coaxially one against the broad face of another and the outermost disc is seated against the shoulders 60 of the knife blade. The disc collection is or can be held in the aforesaid position in the same manner as the discs 12, 16 of the other knife blade 48.

The square ends 84 of the fibre bar 52 preferably are abutted against the confronting faces of the disc 'I6 and the innermost disc 80 of the disc collection and assist the screws B4 and rivets 66 in maintaining the bar and blades in alignment.

The discs 80 are a predetermined small amount less in diameter than the diameter of the cylindrical passage 42 in the nipple 26 and are located therein. The difference in diameter provides an annular passage 86 long in axial length and small in radial thickness through which the pressure gases formed within the interior of the casing i6 upon the blowing of the link 10 on heavy overloads can vent to the atmosph-ere.

The discs 80 and 82 preferably are of metal Cil of good heat conductivity and thereby, in conjunction with the metal nipple 26, abstract heat from the hot gases prior to their liberation into the atmosphere through the passage 46 of the nipple 26. The discs 80 and 82 are preferably thin, for instance, one sixteenth of an inch thick, more or less, depending upon their diameters. The discs 80 and 82 can be about the same thickness and the diameter of the smaller discs 82 can be less than the diameter of the larger discs 80 by about twice the thickness of a disc. These dimensions can be varied within wid-e limits but the proportions given provide annular channels 88 between the large discs, which channels are approximately square in cross-section, as best illustrated in Fig. 7, the channels having considerably larger area than the area of the passage 86 over the edges of the large discs 80. As a result, the high pressure gas passing from the interior of the casing I 6 over the edge of the innermost large disc 8U through the narrow passage 86 discharges into the rst expansion chamber 88 surrounding the first innermost small diameter disc 82. As a consequence of the discharge of high velocity gas discharging from a small orifice into a large chamber, the gas eddies around in the chamber as indicated by the arrows 90, Fig. 7, and has its velocity and energy reduced. Thus the gas pressure in the first chamber is considerably less than the gas pressure in the casing I6. The reduced pressure gas in the rst expansion or eddy chamber flows around the edge of the second large disc 80 and into the second expansion chamber where the pressure and energy are again reduced and so on until the gas issues from the fuse at low velocity. Due to eddying around in the expansion chambers and repeatedly coming in contact with the cool Walls of the chamber, the gas becomes cool and harmless by the time it is finally discharged into the atmosphere.

The outermost large disc 80 is spaced axially from the internal shoulder or flange 44 of the nipple 26 and hence provides a radial gas passage 92 tending to direct the out-flowing gases against the knife blade to further cool the gases.

It will be noted that the removable assembly is clamped to the enclosing casing at one end only of the casing and that the assembly, and especially the fibre bar 52, is free from thrust thereon. With this arrangement the bar receives the oppositely acting forces on the knife blade discs when there is pressure within the casing and supports the discs against endwise displacement, the bar being placed in tension. Since the sets of discs are approximately the same diameter, there is but little tensional force applied to the casing I6. Thus the end ange 44 of the nipple 26 is useful mainly as a gas deflector and to prevent the knife blade 50 from being blown out of the casing if the bar 52 should become burned through on some abnormal circuit interrupting condition.

In Fig. 1, the expansion chambers 88 are conveniently formed by the superposition of alternate large and small discs. The chambers can be formed otherwise, however, and Fig. 8 illustrates a different construction for the right hand end of the fuse. In this gure, the knife blade 50a, corresponding to the blade 50 of Fig. 1, has a disc 94 fixed thereto provided with a cylindrical wall 96 of considerable axial extent confronting and closely spaced from the inner cylindrical face 42a of the nipple 26a. The outer face of the wall is provided with a plurality of axially-spaced annular grooves '98 forming expansion or eddy chambers, with intervening ribs between the chambers closely spaced from the inner face of the nipple. The venting and cooling action of this construction is the same as has been explained in connection with Figs. l through 7.

The venting principle herein described can also be applied to other types of enclosed fuses and Figs. 9, and 11 illustrate various modifications applied to a ferrule-type fuse.

In Fig. 9, the insulating fuse casing |02 is provided with a nipple |04 as before which is int-ernally screw-threaded into the end of the casing and has a projecting part that is externally screwthreaded f and has removably screw-threaded thereon an end cap or ferrule |06 which constitutes a terminal of the fuse and is adapted to be gripped in a ferrule-type of fuse clip. The nipple |04 has an end wall |08 which has an opening I0 therethrough at one side of the axis of the fuse and through which an end I |2 of a fusible link ||4 is extended, the end I I2 being bent over and against the outer face of the end wall '|08 and clamped thereto by the end cap. In some cases the end wall |00 is not integral with the cap carrying member |04 but is, nevertheless, in electrical engagement therewith. The precise manner of supporting the end of the fusible link in engagement with the terminal is not important herein and any desirable construction can be employed.

In accordance with the present invention the end cap |06 is provided with an internal cylindrical and axial chamber |5 having the cylindrical wall H6. A short metal cylinder or thick metal disc ||8 is located within the chamber with its cylindrical wall closely spaced from the chamber Wall H6. The disc wall |20 is provided with a plurality of axially spaced annular grooves forming expansion chambers |22 with intervening ribs |24 so that the pressure gases passing between the walls |i'6 and |20 are caused to expand into and eddy about the chambers, thereby losing energy and temperature. The outermost chamber may be wider axially than the other chambers and is Vented to the atmosphere through a plurality of angularly displaced vent openings |26 passing through the end wall |28 of the end cap.

The disc ||8 may be conveniently secured within the end cap by a rivet |30 passed co axially through the disc and end wall |28, .the head |32 of the rivet lying within the end cap and outstanding beyond the inner face of the disc ||8 and forming a clamping member engaging r the end of the fusible link and pressing it into firm engagement with the end wall |08 of the cap carrying member |04.

In the modification illustrated in Fig. l1, the end cap |36 has the inner face of its end wall |38 formed with annular expansion chambers |40 and intervening annular ribs |42 and closely confronted by a disc |44 iixed by a rivet |46 to the end cap. In this instance, the venting is over the edge of the disc and downward toward the middle of the end cap and outwardly through vents |48 formed in the middle part of the end wall of the cap.

For some purposes the expansion chambers can communicate with each other and be formed as a screw thread especially if the thread is small and of close pitch so that venting lengthwise of the thread is relatively small. Fig. 10 illustrates such a chamber construction wherein theV end cap |40 has internal screw threads |50 which connect the cap with the cap supporting member or nipple |52 of the fuse casing. The cap has a cylindrical disc |54 therein which closely confrontsthe screw threads so that the venting is mainly over the tops of the threads and into the interdental spaces `and axially of the fuse and but slightly in the line of the threads. The gases are finally discharged to the atmosphere through openings |55 in the end wall |58 of the cap. This construction, however, except in special cases is inferior to prior described venting constructions from a manufacturing and performance standpoint.

The present invention discloses but does not claim the invention set forth in my copending application Serial No. 368,018, filed November 30, 1940, now Patent Number 2,280,565, April 21, 1942, in that said application discloses a fuse construction wherein the insulating bar connecting the terminal blades is free from thrust and largely relieves the enclosing casing from tensional forces du'e to gas pressure internally of the casing.

The vent construction herein described permits a relatively thick venting passage 85, or its equivalent, between the confronting parallel surfaces without loss of restriction, so that variation in dimensions of the parts within usual manufacturing tolerances do not materially modify the venting action and the vent is not materially influenced by the nature of the discharged products, or by the accumulation of condensed metal during the progress of the venting action.

I claim:

l. In an electric fuse, the combination of an enclosing casing for the fusible element of the fuse and means to vent the casing of the products of circuit interruption formed upon the melting of the fusible element, said venting means comprising means providing closely spaced generally parallel surfaces providing between them a thin passage open at o-ne end to the interior of the casing and open at the other end exteriorly of the casing, one of said surfaces having a succession of lands alternated with intervening channels and the said passage constraining gas to flow across the tops of the lands and into the intervening channels in succession.

2. In Aan electric fuse, the combination of an enclosing casing and means to vent the casing of the products of circuit interruption including two metal members having closely spaced surfaces forming between them a venting passage open at one end to the interior of the casing and open at the other end exteriorly of 'the casing, at least one of said members having a succession of lands alternated with intervening channels extending transversely of the passage, and the said passage constraining gas to flow across the tops of the lands and into the intervening channels in succession.

3. In an electric fuse, the combination of an enclosing casing, means for venting the casing of the products of circuit interruption including two members having closely spaced confronting surfaces providing between them a vent passage open at one end to the interior of the casing and open at the other end exteriorly of the casing, one of said members being formed of a stack of alternate large and small diameter discs, the small diameter discs providing a succession of channels of relatively large volume open to said passage and alternated with constricted volumes of passage formed in part by the large discs.

4. In a renewable electric fuse, the combination of an enclosing casing, a removable fuse link supporting structure within said casing having a member thereon formed with a succession of grooves and intervening lands, a second mem ber cooperating with said first member and having a surface closely spaced from the grooved surface of said first member and the lands thereof providing a venting passage between the members constraining gas to flow across the tops of the lands and into the intervening grooves in succession, the passage being open to the interior of the casing at one end and open eXteriorly of the casing at the other end, the grooves being out of free communication with each other except through said venting passage and the depth and width of a -groove being much greater than the dimension of the venting passage over a land.

5. In a renewable electric fuse, the combination of an enclosing casing, a removable fuse link supporting structure within said casing including knife blade terminals projecting from the ends of said casing and insulating means connecting said terminals together, said casing at one end having a tubular passage, a member carried by a knife blade terminal having an outer surface which closely confronts the inner surface of said tubular passage and provides between the confronting surfaces a venting passage open at one end to the interior of the said casing and open at the other end exteriorly of the casing, said last named member having its confronting surface formed with a series of grooves open to said passage and spaced lengthwise thereof with intervening lands closely confronting the inner surface of said tubular passage but leaving a thin passage space between them, whereby the passage constrains gas to flow across the tops of the lands and into the intervening grooves in succession.

6. In a renewable electric fuse, the combination of an enclosing casing, a removable fuse link supporting structure within said casing including knife blade terminals projecting from the ends of said casing and insulating means connecting said terminals together, said casing at one end having a tubular passage, a member carried by a knife blade terminal having an outer surface which closely confronts the inner surface of said tubular passage and provides between the confronting surfaces a venting passage open at one end to the interior of said casing and open at the other end exteriorly of the casing, said last named member having its confronting surface formed with a series of grooves open to said passage and spaced lengthwise thereof with intervening lands and comprised of a stack 0f alternate large and small discs.

'7. In a renewable electric fuse, the combination of an enclosing casing having at one end thereof a nipple provided with a tubular passage therein, a removable fuse link supporting structure comprising knife blade end terminals projected through said casing, an insulating support connecting said knife blades, and a member on a knife blade having a cylindrical surface located within the tubular passage of said nipple and closely spaced therefrom providing a venting passage open at one end to the interior of said casing and open at the other end exteriorly of the casing, said member having on its periphery a series of grooves open to said venting passage and disposed in succession lengthwise thereof, with intervening lands between the grooves,

8. In a renewable electric fuse, the combina tion of an enclosing casing having at one end thereof a nipple provided with a tubular passage therein, a removable fuse link supporting structure comprising knife blade end terminals projected through said casing, an insulating support connecting said knife blades, and a member on a knife blade having a cylindrical surface located within the tubular passage of said nipple and closely spaced therefrom providing a venting passage open at one end to the interior of said casing and open at the other end exteriorly of the casing, said member having in its periphery a series of grooves open to said venting passage and disposed in succession lengthwise thereof, with intervening lands between the grooves, said member being comprised of a stack of alternately disposed large and small diameter discs.

9. In an electric fuse, an insulating enclosing casing having a metal nipple on the end thereof provided internally with a cylindrical passage therein, a fuse link supporting structure within said casing having a knife blade terminal extending through said nipple and a member carried by said knife blade within said cylindrical passage having a cylindrical surface closely spaced from said surface of said nipple providing a vent passage open at one end to the interior of the casing and open at the other end exteriorly of the casing, the periphery of said member having a plurality of grooves open to said passage and disposed in succession lengthwise thereof with intervening lands between the grooves.

10. In an electric fuse, an insulating enclosing casing having a metal nipple on the end thereof provided internally with a cylindrical passage therein, a fuse link supporting structure within said casing having a knife blade terminal extending through said nipple and a member carried by said knife blade within said cylindrical passage having a cylindrical surface closely spaced from said surface of said nipple providing a vent passage open at end to the interior of the casing and open at the other end exteriorly of the casing, the periphery of said member having a plurality of grooves open to said passage and disposed in succession lengthwise thereof with intervening lands between the grooves, said last named member being comprised of a stack of alternately large and small diameter discs, the space over a small disc and between adjacent large discs forming an aforesaid groove.

11. A renewable electric fuse comprising a tubular insulating enclosing casing, a nipple fixed to one end of said casing having a tubular passage therein and an inwardly directed flange overlying said passage at one end thereof, a removable fuse link supporting structure located within said casing having knife blade terminals extending through said casing and said nipple, an insulating member connecting said knife blades, a cylindrical member within the tubular passage of said nipple fixed to the associated knife blade having a periphery closely spaced from the wall of said tubular passage and inwardly of the inner face of said flange and providing a venting passage between said member and nipple open to the interior of the casing at one end and open exteriorly of the casing at the other end, the periphery of said member having a plurality of grooves therein open to said passage and spaced lengthwise of said passage with intervening lands between the grooves, and means for clamping said removable structure t0 the other end of said casing with said grooved member in the aforesaid spaced relation with said flange.

12. A renewable electric fuse comprising a tubular insulating enclosing casing, a nipple fixed to one end of said casing having a tubular passage therein and an inwardly directed flange overlying said passage at one end thereof, a removable fuse link supporting structure located within said casing having knife blade terminals extending through said casing and said nipple, an insulating member connecting said knife blades, a cylindrical member within the tubular passage of said nipple xed to the associated knife blade having a periphery closely spaced from the wall of said tubular passage and inwardly of the inner face of said flange and providing a venting passage between said member and nipple open to the interior of the casing at one end and open exteriorly of the casing at the other end, Jthe periphery of said member having a plurality of grooves therein open to said passage and spaced lengthwise of said passage With intervening lands between the grooves, and means for clamping said removable structure to the other end of said casing with said grooved member in the aforesaid spaced relation with said flange, said grooved member being comprised of a stack of alternate large and small diameter discs, a large diameter disc constituting a land and the small diameter disc providing a groove between successive lands.

13. In an electric fuse, the combination of an enclosing casing containing the fusible element, an end cap on the end of the casing having means providing a narrow vent passage open at one end to the interior of the casing and open at the other end exteriorly of the casing, and means providing said passage with a plurality cf successive constrictions and enlargements.

1 14. In an electric fuse, the combination of an enclosing casing, an end cap on the end of said casing, said end cap having members closely spaced from each other providing a venting pas sage open at one end to the interior of the casing and open at the other end exteriorly of the casing, one of said members being provided with a succession of alternate grooves open to and extended transversely of the passage with intervening lands between the grooves.

15. In an electric fuse, an enclosing casing rfor the fusible element, supporting means for the fusible element, and venting means for the products of circuit interruption formed by the fusing of said fusible element under load, comprising means providing a succession of lands alternated with intervening channels, and means closely confronting and spaced from the tops of said lands and overlying the channels and providing a thin passage between it and the tops of the lands constraining gas to flow across the tops of the lands and into the intervening channels in succes-- sion, means providing an entrance from the interior of the casing to one end of said passage, and means providing an exit from the other end of said passage to the atmosphere, the cross sectional area of each of said channels being materially greater than the cross sectional area of the passage.

MORRIS B. WOOD. 

